Method and apparatus for layer 2 ARQ for packets

ABSTRACT

A method and an apparatus are provided for transmitting data by a transmitting apparatus in a communication system. The transmitting apparatus segments a radio link control (RLC) packet data unit (PDU), if an amount of available resources is less than an amount of resources required for retransmitting the RLC PDU. The transmitting apparatus includes polling information in the segmented RLC PDU, if the segmented RLC PDU is a last segmented RLC PDU. The transmitting apparatus transmits the segmented RLC PDU to a receiving apparatus.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 13/712,341, filed in the U.S. Patent and TrademarkOffice (USPTO) on Dec. 12, 2012, which is a Continuation Application ofU.S. patent application Ser. No. 12/117,868, filed in the USPTO on May9, 2008, now U.S. Pat. No. 8,351,380, issued on Jan. 8, 2013, whichclaims priority to a Korean Patent Application filed in the KoreanIntellectual Property Office on May 9, 2007 and assigned Serial No.10-2007-0045243, a Korean Patent Application filed in the KoreanIntellectual Property Office on Sep. 21, 2007 and assigned Serial No.10-2007-0096982, and a Korean Patent Application filed in the KoreanIntellectual Property Office on Apr. 1, 2008 and assigned Serial No.10-2008-0030462, the disclosure of each of which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an Automatic Repeat reQuest(ARQ) method and apparatus in a mobile communication system, and inparticular, to a method and apparatus for preventing small packets frombeing independently transmitted, and guaranteeing transmissionreliability of upper layer packets which are independently transmitted.

2. Description of the Related Art

Since the normal ARQ technique in which a receiver determines whether tosend a retransmission request using a gap between sequence numbers isnot applied to the independently transmitted upper layer packets,reliability of the transmission is guaranteed using polling/timer-basedretransmission.

The term ‘polling/timer-based retransmission’ refers to a technique fortransmitting an indicator for ordering a receiver to report anacknowledgement (ACK) while transmitting a packet that should beguaranteed transmission reliability, and automatically retransmittingthe packet if the acknowledgement is not reported within a predeterminedtime. In this scheme, for each upper layer packet, its reception statusreport is transmitted.

However, in the current service, it is frequent that an upper layerpacket in one direction generates a response packet in the oppositedirection, an exchange of the upper layer packet and its receptionstatus report occurs continuously. For example, referring to FIG. 1, ina Transmission Control Protocol (TCP)-based packet service, a TCP packetor Layer 3 (L3) control request message 115 generates a TCP ACK or L3control response message 120 in the opposite direction to thetransmission direction. The L3 control message is an arbitrary controlmessage generated in an upper layer of Layer 2 (L2), and can be, forexample, a control message of an Internet Protocol (IP) call controlprotocol such as Session Initiation Protocol (SIP), or a controlprotocol of a radio network such as Radio Resource Control (RRC).

With reference to FIG. 2, a description will be made of a situationwhere the exchange of the TCP packet or L3 control request message andthe TCP ACK or L3 control response message is performed in Radio LinkControl (RLC) which is an L2 ARQ protocol.

Referring to FIG. 2, if one RLC device 210 transmits a TCP packet or L3control request message to another RLC device 205 in step 215, the otherRLC device 205 transmits a reception status report for the TCP packet orL3 control request message to the RLC device 210 in step 225. After alapse of a predetermined time, if a TCP ACK or L3 control responsemessage occurs, the other RLC device 205 transmits it to the RLC device210 in step 235, and the RLC device 210 transmits a reception statusreport for the TCP ACK or L3 control response message to the other RLCdevice 205 in step 240.

More specifically, in step 215, the RLC device 205 resegments the TCPpacket or L3 control request message in a size suitable for transmissionthrough a radio channel, attaches a sequence number to the segment, andtransmits the segment through the radio channel. The sequencenumber-attached segment is called an ‘RLC Protocol Data Unit (PDU)’. Inparticular, the RLC device 210, when transmitting the last RLC PDU,includes polling information in the RLC PDU. The polling information isfor requesting the other RLC device to send a reception status report.In order to check the transmission status of the transmitted RLC PDUs,including the last RLC PDU, the RLC device generally transmits the lastRLC PDU along with the polling information.

In preparation for the case where an RLC PDU containing the pollinginformation is lost during its transmission or a status reportresponsive to the polling is lost during its transmission, the RLCdevice 210 performs timer-based retransmission on the RLC PDU containingthe polling information. In other words, the RLC device 210 starts apolling timer 245 while transmitting an RLC PDU containing pollinginformation, and retransmits the RLC PDU containing polling informationif no status report is received until the polling timer expires.

Upon receiving the RLC PDU containing polling information, the RLCdevice 205 generates a status report and transmits the status report tothe RLC device 210 in step 225. At this point, an L2 processing delay220 occurs.

Since TCP data or L3 control request message is included in the RLC PDUcontaining polling information, the TCP data or L3 control requestmessage is delivered to an upper layer. Then the upper layer, after anL3 transmission (processing) delay 230, generates a TCP ACK or L3control response message and delivers it to the RLC device 205. Inresponse, the RLC device 205 generates the TCP ACK or L3 controlresponse message into an RLC PDU and transmits it to the RLC device 210in step 235. Since a size of the TCP ACK or L3 control message is onlyseveral tens of bytes in most cases, it is included in one RLC PDUbefore being transmitted. In other words, since the RLC PDU containingthe TCP ACK or L3 control message is the last RLC PDU, pollinginformation is also included in the RLC PDU before being transmitted. Asa response to the polling, the RLC device 210 transmits an L2 statusreport in step 240.

As described above, the last RLC PDU containing TCP data, as pollinginformation is included therein, induces an L2 status report from theopposite side. The TCP data also causes an L3 response message such asTCP ACK, and the L3 response message such as TCP ACK also causes an L2status report.

Frequently transmitting and receiving the small-sized packets over aradio channel individually in this way may cause a decrease inefficiency of radio transmission resources.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least the problemsand/or disadvantages described above and to provide at least theadvantages described below. Accordingly, an aspect of the presentinvention is to provide a method and apparatus for allowing small-sizedpackets to be transmitted together if possible, rather than beingfrequently transmitted and received over a radio channel individually,thereby increasing efficiency of radio transmission resources.

Another aspect of the present invention is to provide a method andapparatus for guaranteeing transmission reliability of individuallytransmitted upper layer packets without using a reception status report,thereby increasing efficiency of radio transmission resources.

According to one aspect of the present invention, a method is providedfor transmitting data by a transmitting apparatus in a communicationsystem. The transmitting apparatus segments an RLC PDU, if an amount ofavailable resources is less than an amount of resources required forretransmitting the RLC PDU. The transmitting apparatus includes pollinginformation in the segmented RLC PDU, if the segmented RLC PDU is a lastsegmented RLC PDU. The transmitting apparatus transmits the segmentedRLC PDU to a receiving apparatus.

According to another aspect of the present invention, an apparatus isprovided for transmitting data in a communication system. The apparatusincludes a controller configured to segment a RLC PDU for generation ofa segmented RLC PDU, if an amount of available resources is less than anamount of resources required for retransmitting the RLC PDU, and includepolling information in the segmented RLC PDU, if the segmented RLC PDUis a last segmented RLC PDU. The apparatus also includes a transmitterconfigured to transmit the segmented RLC PDU to a receiving apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a diagram illustrating an exemplary exchange of upper layerpackets;

FIG. 2 is a diagram illustrating an exemplary exchange of individuallytransmitted upper layer packets, performed by L2 ARQ protocol;

FIG. 3 is a diagram illustrating a protocol structure of an LTE mobilecommunication system;

FIG. 4 is a signal flow diagram illustrating an overall operationaccording to a first embodiment of the present invention;

FIG. 5 is a signal flow diagram illustrating an operation of an RLCdevice for transmitting polling information according to the firstembodiment of the present invention;

FIG. 6 is a signal flow diagram illustrating an operation of an RLCdevice for receiving polling information according to the firstembodiment of the present invention;

FIG. 7 is a signal flow diagram illustrating an overall operationaccording to a second embodiment of the present invention;

FIG. 8 is a signal flow diagram illustrating an operation of an RLCdevice for transmitting polling information according to the secondembodiment of the present invention;

FIG. 9 is a signal flow diagram illustrating an operation of an RLCdevice for receiving polling information according to the secondembodiment of the present invention;

FIG. 10 is a block diagram illustrating an internal structure of an RLCdevice according to an embodiment of the present invention;

FIG. 11 is a signal flow diagram illustrating an overall operationaccording to a third embodiment of the present invention;

FIG. 12 is a flowchart illustrating an operation of a transmitteraccording to the third embodiment of the present invention;

FIG. 13 is a diagram illustrating a method for performing resegmentedretransmission on a polling PDU so that polling information and only theminimum user data are included;

FIG. 14 is a diagram illustrating resegmented retransmission of apolling PDU;

FIG. 15 is an overall signal flow diagram according to a fourthembodiment of the present invention;

FIG. 16 is a flowchart illustrating an operation of a transmitteraccording to the fourth embodiment of the present invention;

FIG. 17 is an overall signal flow diagram according to a fifthembodiment of the present invention;

FIG. 18 is a flowchart illustrating an operation of a transmitteraccording to the fifth embodiment of the present invention;

FIG. 19 is a diagram illustrating an overall operation of a sixthembodiment of the present invention; and

FIG. 20 is a signal flow diagram illustrating an operation of a terminalaccording to the sixth embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention will now be described in detailwith reference to the annexed drawings. The matters defined in thedescription such as a detailed construction and elements are provided toassist in a comprehensive understanding of exemplary embodiments of theinvention. Accordingly, those of ordinary skill in the art willrecognize that various changes and modifications of the embodimentdescribed herein can be made without departing from the scope and spiritof the invention. Also, descriptions of well-known functions andconstructions are omitted for clarity and conciseness. Terms used hereinare defined based on functions in the present invention and may varyaccording to users, operators' intention or usual practices. Therefore,the definition of the terms should be made based on contents throughoutthe specification.

The present invention provides a method and apparatus for allowingsmall-sized packets to be transmitted together if possible, rather thanbeing frequently transmitted and received over a radio channelindividually, thereby increasing efficiency of radio transmissionresources.

In addition, the present invention provides a method and apparatus forguaranteeing transmission reliability of individually transmitted upperlayer packets without using a reception status report, therebyincreasing efficiency of radio transmission resources.

FIG. 3 illustrates a protocol layer structure of a Long Term Evolution(LTE) communication system to which the present invention is applied.

In a terminal 395 where multiple services are set, as many upper layerdevices as the services and one RRC layer device are established. An RLCdevice is individually constructed in each of the upper layer devicesand RRC layer device.

For example, as shown in FIG. 3, in the terminal 395 where 2 servicesare set, an RRC layer device 305 and upper layer devices 310 and 315,associated individually with the services, are established.

The RRC 305 is a layer for processing a control message associated withradio transmission resources, and the upper layer devices 310 and 315,which are layers serving as L2 interfaces with the services, can be aset of protocols such as, for example, Transmission ControlProtocol/Internet Protocol (TCP/IP) or RTP/UPD/IP. Although notillustrated in the drawing, a separate layer in charge ofencryption/decryption or header compression/decompression can exist inan upper layer of the RLC device. The RRC layer device 305 and the upperlayer devices 310 and 315 associated with their corresponding servicestransmit/receive data interactively, and are connected to RLC devices320, 325 and 330, respectively, which also transmit/receive RLC PDUsinteractively.

The RLC device, as described above, performs a framing operation ofconstructing upper layer data in a size suitable fortransmission/reception through a radio channel, and an ARQ operation forallowing an RLC PDU to be transmitted to the opposite RLC device withreliability. The ARQ operation includes a first process of attaching asequence number to each RLC PDU before transmission, a second process inwhich if a predetermined condition is satisfied, an RLC PDU receivingside notifies acknowledgements of RLC PDUs to an RLC PDU transmittingside, and a third process in which based on the information, the RLC PDUtransmitting side retransmits the reception-failed RLC PDUs. Theacknowledgement information of RLC PDUs and retransmission requestinformation for RLC PDUs will be referred to herein as a ‘statusreport’.

The RLC PDUs generated in the multiple RLC devices are multiplexed intoone packet called a Medium Access Control (MAC) PDU in a MAC layerdevice 335, and then transmitted to a base station 397 via a physicallayer 340.

A MAC layer device 350 of the base station 397 demultiplexes a MAC PDUinto RLC PDUs and delivers the RLC PDUs to proper RLC devices, and theRLC devices each check sequence numbers of the received RLC PDUs todetermine if there is any missing RLC PDU, and if there is a missing RLCPDU, the corresponding RLC device issues a retransmission request forthe missing RLC PDU when a predetermined condition is satisfied. RLCdevices 355, 360 and 365 reassemble the received RLC PDUs in upper layerpackets and deliver them to their associated upper layers. For RRC, anRRC layer device 370 is situated in the base station 397, and for otherservices, it is situated in the opposite end or server, so that the RLCPDU is delivered to upper layers 375 and 380 via a transmission network385.

Generally, the MAC layer device and the RLC layer devices are classifiedas L2, while upper layers of L2 are classified as L3. The term ‘L3 data’as used herein refers to the data generated in upper layers of L2.

First Embodiment

In a first embodiment of the present invention, an RLC device, when ithas received polling information, generates a reception status reportafter waiting a predetermined time without immediately generating thereception status report, if there is a high possibility that an upperlayer packet received along with the polling information will generatean upper layer packet in the opposite direction. If an upper layerpacket occurs during the predetermined waiting time, the RLC devicetransmits a reception status report along with the upper layer packet,thereby preventing the waste of transmission resources caused by theindividual transmission of the reception status report and the upperlayer packet.

The possibility that an arbitrary upper layer packet will generate a newupper layer packet in the opposite direction can be determined accordingto the type of the service connected to the RLC device and/or theproperty of the upper layer packet.

For instance, in the multimedia streaming service among User DatagramProtocol (UDP)-based services, since multimedia data does not generatefeedback data in the opposite direction, an upper layer packet does notgenerate a new upper layer packet in the opposite direction. However, inthe TCP-based service, a TCP ACK occurs for every predetermined numberof TCP segments, there is a high possibility that an upper layer packetwill generate an upper layer packet in the opposite direction. Further,in a control protocol such as RRC, since a request-response basedmessage exchange is generally used, there is a high possibility that anupper layer packet will generate an upper layer packet in the oppositedirection.

In the present invention, the RLC device responds to the pollinginformation with the following two different schemes.

A first polling information-responding scheme, like the conventionalscheme, generates and transmits a reception status report upon receiptof polling information, without waiting for the generation an upperlayer packet.

A second polling information-responding scheme, when it receives pollinginformation, generates and transmits a reception status report afterwaiting a predetermined period, thereby increasing the possibility thatan upper layer packet and a reception status report will be transmittedtogether.

For reference, the situation where polling information is received meansthe situation where the polling information becomes effective as thereordering on an RLC PDU is completed, which was received along with thepolling information or contains polling information.

An RLC device, when transmitting polling information, can transmitinformation indicating which polling information-responding scheme theRLC device will use together with the polling information. Herein,polling information indicating an intension to use the first pollinginformation-responding scheme will be referred to as ‘type-1 pollinginformation’, and polling information indicating an intention to use thesecond polling information-responding scheme will be referred to as‘type-2 polling information’.

Alternatively, every RLC device can be previously set as to whichpolling information-responding scheme it will use. For example, an RLCdevice connected to a UDP-based multimedia streaming service can be setto always use the first polling information-responding scheme, while anRLC device connected to the TCP-based file download service can be setto always use the second polling information-responding scheme.

For the sake of convenience, the last RLC PDU 215 containing pollinginformation and upper layer data having a high possibility that it willcause the generation of upper layer data in the opposite direction willbe referred to as a ‘message #1’; the reception status report 220 whichis a response to the polling information will be referred to as a‘message #2’; the last RLC PDU 235 containing upper layer data in theopposite direction and polling information will be referred to as a‘message #3’; and the reception status report 240 which is a response tothe polling information will be referred to as a ‘message #4’.

In sum, the first embodiment of the present invention transmits themessage #2 and the message #3 together, thereby reducing the resourcewaste caused by the individual transmission of messages. For reference,when individually transmitting small-sized messages, the conventionalRLC device should separately report a buffer status and should beallocated transmission resources every time the RLC device transmits themessages. Therefore, as the size of the messages is smaller, it isinefficient to transmit the messages individually.

FIG. 4 is a signal flow diagram for a description of the firstembodiment of the present invention.

Referring to FIG. 4, an RLC device 410, which is transmitting data in anarbitrary direction, transmits the last RLC PDU at an arbitrary time instep 415. If data included in the RLC PDU is an arbitrary L3 controlrequest message or a TCP segment, the RLC device 410 transmits the RLCPDU along with type-2 polling information. For simpler realization, aterminal and a base station can previously set a polling type for eachradio bearer individually. In this case, an RLC device transmittingpolling information has no need to separately indicate the polling type,and transmits the polling information to the opposite RLC device alongwith the RLC PDU, like the conventional RLC device.

An RLC device 405 which has received the RLC PDU along with the type-2polling information, or an RLC device 405 which has received an RLC PDUalong with polling information and is set to use the second pollinginformation-responding scheme, starts a predetermined timer T1 (See420), and then reassembles the upper layer data from the RLC PDU anddelivers it to an upper layer. If T1 expires or if new data arrives fromthe upper layer even though T1 has not expired, the RLC device 405starts a procedure for transmitting a reception status report and upperlayer data. That is, the RLC device 405 transmits to a scheduler abuffer status report for requesting allocation of transmission resourcesfor transmission of the reception status report and upper layer data,and is allocated transmission resources from the scheduler. Then the RLCdevice 405 transmits a status report and upper layer data together usingthe allocated transmission resources in step 425. If all of the upperlayer data is included one RLC PDU, the RLC device 405 includes pollinginformation in the RLC PDU before transmission in order to checksuccessful transmission of the RLC PDU. Upon receiving the RLC PDU andpolling information, the RLC device 410 generates a reception statusreport indicating successful receipt of the RLC PDU and transmits it tothe opposite RLC device 405 in step 430.

As described above, when the RLC PDU containing data having a highpossibility that it will cause generation of upper layer data in theopposite direction is received along with polling information, theembodiment allows the RLC device to generate a reception status reportafter waiting a predetermined time, thereby increasing the possibilitythat the reception status report and upper layer data will betransmitted together.

FIG. 5 is a signal flow diagram illustrating an operation of an RLCdevice for transmitting polling information according to the firstembodiment of the present invention.

In step 505, an RLC device recognizes a use condition of type-2 pollinginformation. The type-2 polling information is used when there is a highpossibility that data contained in an RLC PDU transmitted along with thepolling information will cause an upper layer response message, and thetype-2 polling information use condition can be defined as follows, byway of example.

An upper layer designates a polling type to use, and notifies choice tothe RLC device. Among L3 control messages such as an RRC message, somemessages are request messages causing response messages, while someother messages are request messages not needing any accompanyingresponse messages. Since the RLC device cannot determine whether anarbitrary RRC message will cause a response message, when the RRCmessage is a request message causing a response message, an RRC devicesends this indication to the RLC device, and the RLC device uses type-2polling information only when it receives the indication from the upperlayer device, and otherwise, uses type-1 polling information.

When the polling information-responding scheme the RLC device will useduring call setup is previously determined, the transmission sidetransmitting polling information has no need to especially distinguishthe polling information type. For example, if an RLC device connected toa TCP-based service is set to use the second pollinginformation-responding scheme, an RLC device transmitting pollinginformation uses normal polling information while an RLC devicereceiving polling information recognizes all polling information astype-2 polling information. Therefore, the operation shown in FIG. 5 isapplied when the polling information-responding scheme to be usedindividually for each RLC device is not previously determined.

The type-2 polling information use condition can be notified to the RLCdevice during call setup.

When an RLC device is constructed through a call setup process, the RLCdevice exchanges RLC PDUs with the opposite RLC device through apredetermined procedure.

Referring back to FIG. 5, in step 510, the RLC device triggers pollingas a predetermined condition is satisfied. The polling can be triggeredin several conditions, and can be triggered, for example, when the lastRLC PDU stored in a transmission buffer is transmitted.

The RLC device determines in step 515 whether there is a highpossibility that upper layer data contained in an RLC PDU to betransmitted along with polling information will cause an upper layerresponse message in the opposite direction. In other words, the RLCdevice determines if the type-2 polling information use condition issatisfied. If it is determined in step 515 that the type-2 pollinginformation use condition is unsatisfied, the RLC device delivers an RLCPDU containing the type-1 polling information to a lower layer in step520, like the conventional RLC device, and the lower layer transmits thetype-1 polling information and RLC PDU.

However, if it is determined in step 515 that the type-2 pollinginformation use condition is satisfied, the RLC device delivers an RLCPDU containing the type-2 polling information to a lower layer in step525, and the lower layer transmits the type-2 polling information andRLC PDU.

FIG. 6 is a signal flow diagram illustrating an operation of an RLCdevice for receiving polling information according to the firstembodiment of the present invention.

In step 605, an RLC device recognizes a T1 timer value. The T1 timervalue should be set to a value corresponding to the L3 processing delay230, and the network determines the T1 timer value taking into account acharacteristic of the call established in the call setup process, andnotifies it to the RLC device.

If an RLC device is constructed through the call setup process, the RLCdevice exchanges RLC PDUs with the opposite RLC device through apredetermined procedure.

If the RLC device receives polling information in step 610, the RLCdevice proceeds to step 615 where it checks a type of the receivedpolling information. If the received polling information is type-2polling information, the RLC device proceeds to step 620 where it startsthe T1 timer, and then proceeds to step 625, if the T1 timer expires.Otherwise, if upper layer data arrives even before the T1 timer expires,the RLC device can immediately proceeds to step 625. In step 625, theRLC device starts a reception status report transmission process inresponse to the polling information. In other words, the RLC devicenotifies the lower layer of a size of the reception status reportmessage. If upper layer data has arrived while the T1 timer runs, a sizeof the upper layer data is also notified together. The lower layer sendsa request for allocation of transmission resources to a schedulerdepending on the data size, and if transmission resources are allocated,the lower layer determines a size of the data the RLC device willtransmit, based on the allocated transmission resources. At the sametime, the lower layer notifies the RLC device of the size of thetransmission data. If the RLC device is notified of the size of thetransmission data from the lower layer in step 635, the RLC devicegenerates a reception status report and RLC PDU corresponding to thesize and delivers it to the lower layer in step 640. The lower layertransmits the RLC PDU and reception status report to the opposite RLCdevice.

However, if it is determined in step 615 that the received pollinginformation is the type-1 polling information which is equal to theconventional one, the RLC device proceeds to step 630 where itimmediately starts a reception status report transmission processwithout the waiting time set in the T1 timer. That is, the RLC devicereports the size of the reception status report message to the lowerlayer. If the lower layer issues an order to generate and transmit anRLC PDU having a predetermined size in step 635, the RLC device includesa reception status report message in an RLC PDU and delivers it to thelower layer in step 640.

When the polling information-responding scheme the RLC device will usein a call setup process is previously determined, the decision operationof step 615 is not needed, since the RLC device determines the receivedpolling information as polling information corresponding to thepredetermined polling information-responding scheme.

In other words, an RLC device predetermined to use the first pollinginformation-responding scheme undergoes steps 605, 610, 630, 635 and640, while an RLC device predetermined to use the second pollinginformation-responding scheme undergoes steps 605, 610, 620, 625, 635and 640.

Second Embodiment

A second embodiment of the present invention provides a method andapparatus for, when a reception status report and upper layer data aretransmitted together, determining a success/failure in the transmissionof the upper layer data transmitted along with the reception statusreport based on retransmission/non-retransmission of polling informationwhich has caused the reception status report. The use of the secondembodiment of the present invention can guarantee reliability of thetransmission even without making a separate reception status report onthe upper layer data, making it possible to save the transmissionresources.

As stated above, the reliability of polling information is guaranteed bythe timer-based retransmission technique. An RLC device transmittingpolling information starts a polling timer, and retransmits the pollinginformation if it fails to receive a reception status report responsiveto the polling information until the timer expires.

Then, an RLC device, which has transmitted a reception status reportafter receiving the polling information, can determine that thereception status report has been successfully transmitted, if it doesnot receive again the polling information for a predetermined period. Ifthe RLC device has transmitted the reception status report and upperlayer data together, the success/failure in the transmission of thereception status report is coincident with the success/failure in thetransmission of the upper layer data. Therefore, by linkingretransmission of the upper layer data to retransmission of thereception status report, it is possible to guarantee reliability of theupper layer data even without receiving a separate status report fromthe opposite RLC device. Although this operation cannot be widelyapplied since it is limited to the upper layer data transmitted alongwith a reception status report, it can be usefully used when small-sizedupper layer data such as TCP ACK and RRC control response message istransmitted on a temporary basis.

FIG. 7 is a signal flow diagram illustrating an operation according tothe second embodiment of the present invention.

An RLC device 710, which is transmitting data in an arbitrary direction,transmits the last RLC PDU at an arbitrary time. If data contained inthe RLC PDU is an arbitrary L3 control request message or TCP segment,the RLC device 710 transmits the RLC PDU along with type-2 pollinginformation in step 715. For simpler realization, a terminal and a basestation can previously set a polling type for each radio bearerindividually. In this case, an RLC device transmitting pollinginformation has no need to separately indicate the polling type, andtransmits the polling information to the opposite RLC device along withthe RLC PDU, like the conventional RLC device. The RLC device 710 startsa polling timer (as in Step 720), after the transmission of pollinginformation is completed.

Upon receiving the type-2 polling information and RLC PDU, an RLC device705 starts a predetermined timer T1 and starts a data transmissionprocedure after the T1 expires, as done in the first embodiment of thepresent invention. If upper layer data has arrived while the T1 timerruns, both the reception status report and the upper layer data areincluded in a buffer status report made through the data transmissionprocedure. Further, transmission resources are allocated fortransmission of the reception status report and upper layer data.

The RLC device 705 transmits a reception status report and an RLC PDUcontaining upper layer data using the allocated transmission resourcesin step 725. The upper layer data contained in the RLC PDU can be, forexample, TCP ACK or L3 control response message.

The RLC device 705 uses a T2 timer in order to determine thesuccess/failure in transmission of the RLC PDU transmitted along withthe reception status report. If polling information, i.e., message #1,is retransmitted in step 745, which caused the reception status reporttransmitted along with RLC PDU, before the T2 timer expires, the RLCdevice 705 retransmits the reception status report and RLC PDU, since itmeans that the transmission of the reception status report and the RLCPDU transmitted along with the reception status report has failed.However, if the polling information, i.e., message #1, is notretransmitted, which caused the reception status report transmittedalong with the RLC PDU, until the T2 timer expires, the RLC devicediscards the RLC PDU from the retransmission buffer, considering thatthe transmission of the reception status report and the RLC PDUtransmitted along with the reception status report is made successfully.

In order to prevent mal-operation of the RLC device, it is necessary toappropriately set the T2 timer value. If the T2 timer expires before theexpiration of the polling timer, the RLC device may misrecognize thetransmission as a successful transmission, even though the transmissionof the reception status report and its associated (coupled) RLC PDU hasfailed. On the other hand, if the T2 timer expires considerably laterthan the expiration of the polling timer, the RLC device shouldunnecessarily store the coupled RLC PDU in its retransmission buffer.Therefore, it is preferable that the expiration of the T2 timer slightlyfalls behind the expiration of the polling timer, and to this end, astart of the T2 timer needs to be linked with a start of the pollingtimer. For example, if a start time of the polling timer is a time thatthe transmission of the polling information is completed, the T2 timeris also started at a time 730 when the RLC device 705 receives thepolling information. However, if an RLC device receiving the pollinginformation cannot estimate a start time of the polling timer, the RLCdevice starts the T2 timer at a time 733 when the transmission of thereception status report and its associated RLC PDU is completed.

As described above, the second embodiment of the present inventiondetermines the success/failure in the transmission of the coupled RLCPDU depending on the success/failure in the transmission of thereception status report, thereby making it possible to guaranteetransmission reliability of the RLC PDU even without receiving aseparate reception status report on the coupled RLC PDU.

FIG. 8 is a signal flow diagram illustrating an operation of an RLCdevice for transmitting polling information according to the secondembodiment of the present invention.

Referring to FIG. 8, in step 805, an RLC device recognizes a pollingtimer value and a use condition of type-2 polling information. Thetype-2 polling information use condition is equal to that in the firstembodiment, so a description thereof will be omitted herein. The pollingtimer value is for the retransmission of the polling information, andafter transmitting the polling information, the RLC device starts thepolling timer, and retransmits the polling information if no receptionstatus report responsive to the polling timer is received before thepolling timer expires.

The type-2 polling information use condition and polling timer value canbe notified to the RLC device during call setup. If an RLC device isconstructed through a call setup process, the RLC device exchanges RLCPDUs with the opposite RLC device through a predetermined procedure.

In step 810, the RLC device triggers polling as a predeterminedcondition is satisfied. There are several possible conditions fortriggering the polling, and the polling can be triggered, for example,when the last RLC PDU stored in a transmission buffer is transmitted.

The RLC device determines in step 815 whether there is a possibilitythat upper layer data contained in an RLC PDU to be transmitted alongwith polling information will cause an upper layer response message inthe opposite direction. In other words, the RLC device determines if thetype-2 polling information use condition is satisfied.

If it is determined in step 815 that the type-2 polling information usecondition is unsatisfied, the RLC device delivers an RLC PDU containingtype-1 polling information to a lower layer and the lower layertransmits the type-1 polling information and RLC PDU in step 820, andthen proceeds to step 830.

However, if it is determined in step 815 that the type-2 pollinginformation use condition is satisfied, the RLC device delivers an RLCPDU containing type-2 polling information to a lower layer and the lowerlayer transmits the type-2 polling information and RLC PDU in step 825,and then proceeds to step 830.

In step 830, the RLC device starts the polling timer, and monitorsreceipt of a reception status report responsive to the pollinginformation. If no reception status report is received until the timerexpires, the RLC device proceeds to step 835 where it retransmits theRLC PDU containing polling information and starts the polling timer. TheRLC device repeats the operation of step 835 until a reception statusreport is received or a predetermined condition is satisfied.

FIG. 9 is a signal flow diagram illustrating an operation of an RLCdevice for receiving polling information according to the secondembodiment of the present invention.

In step 905, an RLC device recognizes a T1 timer value and a T2 timervalue. The T1 timer is equal to that in the first embodiment, so adescription thereof will be omitted herein. The T2 timer value, asdescribed above, should be set such that it has a slightly longer valuethan the polling timer on the assumption that the T2 timer and thepolling timer are started at the similar time. A call setup controldevice of the network determines the T1 timer value and the T2 timervalue taking a property of the call into consideration during callsetup, and sends the timer values to a terminal and a base station, andthe terminal and the base station each establish RLC devices and deliverthe timer values to the RLC devices.

When an RLC device is constructed through a call setup process, the RLCdevice exchanges RLC PDUs with the opposite RLC device through apredetermined procedure.

If the RLC device receives type-2 polling information in step 910, theRLC device proceeds to step 920 where it starts the T1 timer andproceeds to step 925 if the T1 timer expires. If upper layer data hasarrived even before the T1 timer expires, the RLC device can immediatelyproceed to step 925.

In step 925, the RLC device starts a reception status reporttransmission process in response to the polling information. That is,the RLC device notifies the lower layer of a size of the receptionstatus report message. If upper layer data has arrived while the T1timer runs, the RLC device notifies a size of the upper layer data aswell. The lower layer sends a request for allocation of transmissionresources to a scheduler depending on the data size. When transmissionresources are allocated, the RLC device determines the amount oftransmission data based on the allocated transmission resources.

In step 935, the lower layer notifies the RLC device of the amount oftransmission data. In step 940, the RLC device generates a receptionstatus report, and if there is upper layer data, generates an RLC PDUwith the upper layer data, and then delivers them to the lower layer.

For the sake of convenience, the RLC PDU transmitted along with thereception status report will be referred to herein as a ‘coupled RLCPDU’. The lower layer transmits the coupled RLC PDU and reception statusreport to the opposite RLC device.

In step 945, the RLC device monitors if the polling information whichcaused the reception status report transmitted along with the coupledRLC PDU is retransmitted before the T2 timer expires.

The T2 timer can be started in step 910 where the RLC device receivedthe type-2 polling information, or can be started at the time that thetransmission of the coupled RLC PDU is completed. The situation wherethe polling information is not retransmitted until the T2 timer expiresmeans that the coupled RLC PDU has been successfully transmitted, whilethe situation where the polling information is retransmitted means thatthe transmission of the coupled RLC PDU has failed.

The followings are methods for determining if arbitrary pollinginformation is polling information that has caused the reception statusreport transmitted along with the coupled RLC PDU.

If polling information is transmitted after being included in an RLCPDU, a sequence number of the RLC PDU can be used as an identifier ofthe polling information. That is, if a sequence number of an RLC PDU inwhich polling information received at an arbitrary time is included isidentical to a sequence number of an RLC PDU in which previouslyreceived polling information is included, it means that the pollinginformation is the same and it can be determined that the presentlyreceived polling information is the retransmitted information of thepreviously received polling information.

For simple realization, all type-2 polling information received before aT2 timer expires can be regarded as retransmitted information of type-2polling information which has caused a start of the T2 timer.

Referring back to FIG. 9, if it is determined in step 945 thattransmission of the reception status report and coupled RLC PDU hasfailed, the RLC device retransmits the coupled RLC PDU and receptionstatus report in step 950. In this case, a reception status reportupdated with reception status information at the corresponding time canbe retransmitted.

However, if it is determined in step 945 that the transmission of thereception status report and coupled RLC PDU is made successfully, theRLC device deletes the coupled RLC PDU from a retransmission buffer instep 955, and then ends the procedure.

FIG. 10 is a block diagram illustrating an internal structure of an RLCdevice according to an embodiment of the present invention.

Referring to FIG. 10, an RLC device 1000 includes a transmissioncontroller 1005, a transmission buffer 1010, a framing unit 1015, aretransmission buffer 1020, a reception status report processor 1040, areception buffer 1045, and a polling information processor 1055.

The RLC device is connected to a multiplexer 1025 and a demultiplexer1050. The multiplexer 1025 multiplexes RLC PDUs provided from multipleRLC devices into one Hybrid ARQ (HARQ) packet. The demultiplexer 1050demultiplexes an HARQ packet provided from an HARQ processor, anddelivers the results to a proper RLC device.

An HARQ processor 1030 is a device for transmitting/receiving HARQpackets through a predetermined HARQ operation, and a transceiver 1035is a device for modulating HARQ packets into a radio transmission signaland demodulating a received radio signal.

A detailed description will now be made of an operation of the RLCdevice 1000. Data provided from an upper layer is stored in thetransmission buffer 1010, and later framed into an RLC PDU with a propersize under the control of the transmission controller 1005. Thetransmission controller 1005 reports the amount of desired transmissiondata to the lower layer, receives from the lower layer a notificationindicating the amount of data the lower layer will transmit in the nexttransmission period, and determines the data it will transmit in thenext transmission period according to the amount of transmission data.

The amount of desired transmission data is determined by taking intoaccount all of (i) the amount of data stored in the transmission buffer1010, (ii) the amount of data stored in the retransmission buffer 1020,and (iii) a size of other control information such as a reception statusreport.

The transmission controller 1005 starts a T1 timer upon receipt oftype-2 polling information, and if the T1 timer expires, controls thereception status report processor 1040 so as to generate a receptionstatus report. When transmission of the reception status report andcoupled RLC PDU is completed, the transmission controller 1005 starts aT2 timer. If no type-2 polling information is received until the T2timer expires, the transmission controller 1005 removes coupled RLC PDUfrom the retransmission buffer 1020, determining that the transmissionof the coupled RLC PDU is made successfully. If type-2 pollinginformation is received before the T2 timer expires, the transmissioncontroller 1005, determining that the transmission of the coupled RLCPDU and reception status report has failed, controls the receptionstatus report processor 1040 to generate a new reception status reportand retransmits the reception status report and coupled RLC PDU.

The framing unit 1015 makes an RLC PDU by attaching an RLC header to thedata provided from the transmission buffer 1010. The RLC PDU isdelivered to the multiplexer 1025 and stored in the retransmissionbuffer 1020, and the RLC PDU stored in the retransmission buffer 1020 isretransmitted at the request of the opposite RLC device, or removed whenit is determined that the corresponding RLC PDU has been successfullytransmitted.

The polling information processor 1055 includes polling information inan RLC PDU before transmission if a predetermined condition issatisfied. Also, the polling information processor 1055 recognizes atype-2 polling information triggering condition, transmits type-2polling information when the condition is satisfied, and transmitstype-1 polling information when the condition is not satisfied. Uponreceipt of polling information, the polling information processor 1055notifies it to the transmission controller 1005.

An RLC PDU provided from the demultiplexer 1050 is stored in thereception buffer 1045, and the reception status report processor 1040,if a predetermined status report generation condition is satisfied,reports to the transmission controller 1005 that it should transmit astatus report. If the transmission controller 1005 issues a statusreport transmission order, the reception status report processor 1040checks sequence numbers of RLC PDUs stored in the reception buffer 1045,recognizes successfully received RLC PDUs and sequence numbers ofretransmission-requested RLC PDUs, generates a reception status reportaccording thereto, and transmits the generated reception status report.

In a third embodiment, the transmission controller managesretransmission of polling information. If there is a need forretransmission of the polling information due to the expiration of apolling timer, the transmission controller controls the retransmissionbuffer and the framing unit so as to resegment a polling PDU stored inthe retransmission buffer using a predetermined method, and to newlygenerate a polling PDU containing the polling information and only theminimum user data. The polling PDU containing the polling informationand only the minimum user data is transmitted by way of the multiplexer,the HARQ processor, and the transceiver. If there is a need forretransmission of the polling PDU for a reason other than the expirationof the polling timer, for example, due to a transmission failure for thepolling PDU in an HARQ level, the transmission controller controls theretransmission buffer so as to retransmit the polling PDU stored in theretransmission buffer according to the original retransmissionprocedure. In other words, if transmission resources, the amount ofwhich is sufficient for retransmission of the original polling PDU, areavailable at this moment, the transmission controller retransmits thepolling PDU as it is, and if the transmission resources areinsufficient, the transmission controller resegments the polling PDU ina transmittable size before transmission.

In a fourth embodiment, the transmission controller managesretransmission of polling information. If there is a need forresegmented retransmission of a polling PDU, the transmission controllerchecks a trigger of the polling information, and controls the pollinginformation processor according to the trigger so that the pollinginformation is included in the first segment or the last segment.

In a fifth embodiment, the transmission controller managesretransmission of polling information. The transmission controllerstarts a predetermined polling timer at the time it first receives apacket from the opposite RLC device after a lapse of a time of T3 aftera polling PDU was successfully transmitted. If no reception statusreport message is received until the polling timer expires, thetransmission controller starts a retransmission procedure of pollinginformation.

Third Embodiment

The third embodiment of the present invention provides a method forretransmitting an RLC PDU containing polling information in such amanner that the method retransmits the RLC PDU along with the pollinginformation when there is a high possibility that the RLC PDU containingpolling information might be lost, and the method retransmits only thepolling information when, even though the RLC PDU containing pollinginformation was normally transmitted, there is a high possibility that areception status report message might be lost. More specifically, inretransmission due to HARQ transmission failure for the RLC PDUcontaining polling information, the method retransmits the entire RLCPDU containing polling information, and when retransmission is neededbecause even though the HARQ transmission for the RLC PDU containingpolling information was made successfully, no reception status report isreceived until the polling timer expires, the method retransmits onlythe polling information.

FIG. 11 is a signal flow diagram illustrating an overall operationaccording to the third embodiment of the present invention.

In a mobile communication system including a device 1110 fortransmitting polling information (hereinafter referred to as a‘transmitter’) and a device 1105 for receiving polling information(hereinafter referred to as a ‘receiver’), the transmitter 1110transmits an RLC PDU containing polling information if a predeterminedcondition is satisfied. A condition of generating polling information iscalled a ‘polling information generation condition’ (or ‘pollingtriggering condition’), and a definition thereof is given as follows, byway of example.

The polling triggering condition can be satisfied when:

-   -   the last data is transmitted, which is stored in a transmission        buffer or a retransmission buffer (First Triggering Condition);    -   a predetermined timer, which was started after transmission of        polling information, expires (Second Triggering Condition); and    -   the amount of outstanding RLC PDU stored in the retransmission        buffer exceeds a predetermined ratio of the total buffer size to        the amount of outstanding RLC PDU (Third Triggering Condition).

Among the RLC PDUs being transmitted to the opposite RLC device, an RLCPDU, successful transmission of which is not yet checked, i.e., an RLCPDU for which no positive acknowledgement (ACK) is received from theopposite RLC device, is called an ‘outstanding RLC PDU’.

The triggering condition can be differently set for each RLC device. Forexample, an arbitrary RLC device can be set to respond to only the firsttriggering condition, while other RLC devices can be set to respond tothe first and third triggering conditions.

If the polling triggering condition is satisfied, the transmittergenerates an RLC PDU by concatenating an RLC header to a payload, anddelivers the RLC PDU to a lower layer. The payload contains user dataand/or RLC control information provided from an upper layer. The pollinginformation can be defined as a particular field of the RLC header, orcan be defined as separate RLC control information. An RLC PDUcontaining polling information is defined as a polling PDU regardless ofhow the polling information is defined. Upon receiving the RLC PDU, thelower layer transmits RLC PDU through a predetermined HARQ operation.According to the property of the HARQ operation, the lower layer canrelatively correctly recognize the success/failure in transmission ofthe RLC PDU.

The HARQ operation performs an ARQ operation in which an HARQtransmitting side and an HARQ receiving side are simplified, and if anHARQ transmitter has received a positive acknowledgement in an HARQlevel (hereinafter referred to as ‘HARQ ACK’) for a packet containing aparticular RLC PDU, the HARQ transmitter can determine that thecorresponding RLC PDU has been successfully transmitted. If the HARQtransmitter has failed to receive HARQ ACK for the packet containing RLCPDU despite of a predetermined number of retransmissions, the HARQtransmitter can determine that the transmission of the corresponding RLCPDU has failed. The HARQ ACK or HARQ negative acknowledgement (NACK) issubject to distortion during transmission/reception, and in this case,the HARQ device cannot correctly determine the success/failure intransmission. In other words, unless the HARQ ACK signal or the HARQNACK signal is distorted, the HARQ device can correctly determine thesuccess/failure in transmission of a particular packet. Generally, inthe radio channel environment, a probability that an HARQ NACK signalwill be distorted into an HARQ ACK signal is about 10e-3˜10e-4. In otherwords, a probability that a packet, whose transmission is determined tobe successful in the HARQ level, would not be successfully transmittedin actuality is about 10e-3˜10e-4. A probability that despite of apredetermined number of retransmissions, no HARQ ACK has occurred for anarbitrary HARQ packet is about 10e-2. For the sake of convenience, thesituation where even though an arbitrary packet has been retransmitted apredetermined number of times, no HARQ ACK is received for the packet isreferred to as ‘transmission of the packet in the HARQ level is failed’.

If a lower layer performing HARQ transmission has failed in transmissionof a packet in which a polling RLC PDU 1115 containing pollinginformation is included, the lower layer notifies the transmissionfailure for the RLC PDU to the transmitter (as in Step 1120).

Upon receiving the notification indicating the transmission failure forthe polling RLC PDU from the lower layer, the transmitter retransmitsthe entire polling PDU (as in Step 1125), determining that the RLC PDUcontaining polling information is totally lost.

If the transmission in the HARQ level for the retransmitted packetcontaining polling RLC PDU is made successfully, the lower layernotifies the transmitter of the success in transmission of the RLC PDU(as in Step 1130). After receiving the notification indicating thetransmission success, the transmitter starts a polling timer at anarbitrary time (as in Step 1135), and performs retransmission of thepolling information if it fails to receive a reception status reportuntil the polling timer expires. As stated above, a probability thateven though the HARQ device has determined that the transmission ofpolling PDU was made successfully, the polling PDU would not besuccessfully transmitted in actuality is about 10e-3˜10e-4. However, aprobability that the transmission of the status report message would befailed is about 10e-2. In other words, the loss probability of thestatus report message is much greater than the loss probability of thepolling PDU. In this situation, therefore, the transmitter retransmitsonly the polling information (as in Step 1140), rather thanretransmitting the entire polling PDU.

FIG. 12 is a flowchart illustrating an operation of a transmitter.

If the foregoing polling triggering condition is satisfied in step 1205,a transmitter generates an RLC PDU containing polling information anddelivers it to a lower layer in step 1210. The RLC PDU is composed of aheader and a payload, and the polling information can be contained in apredetermined header field, or can be contained in a payload as aseparate RLC control message. Also, a part of an RLC PDU which is userdata provided from an upper layer is contained in the payload. Thetransmitter determines in step 1215 if the RLC PDU containing pollinginformation has been successfully transmitted in an HARQ level. If anHARQ ACK is received for a packet in which the RLC PDU containingpolling information is included, it means that the RLC PDU has beensuccessfully transmitted in the HARQ level, and if the transmitter hasfailed to receive HARQ ACK even though it has transmitted andretransmitted the packet including the RLC PDU containing pollinginformation a predetermined number of times, it means that the RLC PDUcontaining polling information has failed in the transmission in theHARQ level. If the RLC PDU containing polling information has beensuccessfully transmitted in the HARQ level, the transmitter proceeds tostep 1225, and if the RLC PDU containing polling information has failedin transmission in the HARQ level, the transmitter proceeds to step1220.

In step 1220, the transmitter performs retransmission on the RLC PDUcontaining polling information. That is, the transmitter delivers theRLC PDU containing polling information back to the lower layer, and thenreturns to step 1215 where the transmitter determines whether the RLCPDU has been successfully transmitted in the HARQ level.

If the RLC PDU containing polling information has been successfullytransmitted in the HARQ level, the transmitter proceeds to step 1225where it starts a polling timer. In step 1230, the transmitterdetermines if a reception status report is received before the pollingtimer expires. If no reception status report is received until thepolling timer expires, the transmitter proceeds to step 1235. Proceedingto step 1230 means that the polling PDU, which has been successfullytransmitted in the HARQ level, has failed in transmission in reality dueto distortion of the HARQ feedback information, or the transmission ofthe reception status report message responsive to the pollinginformation has failed. Since the transmission failure probability dueto the distortion of the HARQ feedback information is much less than thetransmission failure probability of the reception status report messageas described above, the transmitter determines that the transmission ofthe reception status report message has failed. The terminal,determining that the polling PDU has been successfully transmitted,retransmits only the polling information without retransmitting the userdata included in the payload of the polling PDU.

If the polling information is defined as a separate RLC control message,it is naturally possible to retransmit only the polling informationwithout retransmitting the user data. However, if the pollinginformation is defined as a predetermined field of the RLC header, thetransmitter performs resegmented retransmission separately only on thelast byte in the payload of the RLC PDU containing polling information,or performs resegmented retransmission only on the RLC header withoutincluding the payload. The term ‘resegmented retransmission’ refers toan operation of resegmenting and retransmitting only a part of the RLCPDU when the terminal cannot retransmit the entire RLC PDU astransmission resources allocated to the terminal are insufficient at thetime the retransmission of the particular RLC PDU is needed. However,since there is a high probability that the polling PDU has beensuccessfully transmitted, it is possible to minimize the amount of userdata transmitted along with the polling information, by using theresegmented retransmission technique even when it is necessary toretransmit only the polling information.

More specifically, referring to FIG. 13, lets it is assumed that asequence number of a header in an RLC PDU 1315 composed of an RLC header1305 and a payload 1310 is set as ‘x’ and a poll bit is set as ‘yes’before being transmitted. If the RLC PDU has been successfullytransmitted in the HARQ level but should be retransmitted as noreception status report is received before the polling timer expires,the transmitter resegments and retransmits only the last byte 1330 inthe payload of the RLC PDU. That is, the transmitter includes the lastbyte in the payload part, inserts the same sequence number x as that ofthe original RLC PDU into the RLC header, and sets the poll bit as‘yes’. The PDU is a PDU which is subject to resegmented retransmission,and a resegmentation header 1325 is inserted therein so that the PDU canlater be reassembled into the original PDU. Offset informationindicating a position of the payload undergoing resegmentedretransmission in the original payload is included in the resegmentationheader, and information indicating that the payload undergoingresegmented retransmission is the last byte of the original payload isincluded in the offset information. For example, if the full size of theoriginal payload is assumed to be K bytes, [K−1] is contained in theoffset. Further, the transmitter sets a flag Last_Segment_Flagindicating the last segment as ‘yes’. Alternatively, it is also possibleto never include user data in the RLC PDU undergoing resegmentedretransmission. In generating an RLC PDU including no payload, thetransmitter inserts the same sequence number x as that of the originalRLC PDU into a header of the RLC PDU, and sets the poll bit as ‘yes’. Inaddition, the transmitter includes a payload size K of the original PDUin an offset field of the resegmentation header of the RLC PDU, and setsthe flag indicating the last segment as ‘yes’. The use of theresegmented retransmission technique can minimize the amount of userdata retransmitted along with the polling information.

Upon receiving a reception status report before the polling timerexpires, the transmitter ends the polling information transmissionprocess.

Fourth Embodiment

The fourth embodiment of the present invention provides a method forincluding polling information in different segments according to atriggering condition of a polling PDU during resegmented retransmissionof the polling PDU. The term ‘resegmented retransmission’ means anoperation of resegmenting a particular RLC PDU into several segments andretransmitting the segments. The resegmented retransmission isimplemented when it is not possible to transmit the original RLC PDU asit is, because, for example, a channel condition of a terminal is pooror the amount of generated traffic increases at a retransmission time.If polling information was contained in the original RLC PDU, it isdesirable to include polling information even in the RLC PDU undergoingretransmission. However, since including polling information in allsegments undergoing resegmented retransmission may cause themore-than-necessary reception status report messages, it is preferableto include polling information only in some of the segments undergoingresegmented retransmission.

The fourth embodiment of the present invention includes pollinginformation in the segment that can best satisfy a purpose of thepolling information, according to the causes of generating the pollinginformation.

As described above, the polling triggering condition can be satisfiedwhen:

-   -   the last data is transmitted, which is stored in a transmission        buffer or a retransmission buffer (hereinafter referred to as        ‘last RLC PDU trigger’);    -   a predetermined timer, which was started after transmission of        polling information, expires (hereinafter referred to as        ‘periodic trigger’); and    -   the amount of outstanding RLC PDU stored in the retransmission        buffer exceeds a predetermined ratio of the total buffer size to        the amount of outstanding RLC PDU (hereinafter referred to as        ‘window trigger’).

As an example shown in FIG. 14, it is assumed that transmission of anRLC PDU 1405 containing polling information 1430 has failed, and the RLCPDU 1405 is subject to resegmented retransmission after resegmented intomultiple RLC PDUs 1415, 1420 and 1425.

If the polling information is generated by the last RLC PDU trigger, apurpose of the polling information is that a transmitter receives areception status report for reception status of all RLC PDUs, includingthe last RLC PDU. Therefore, when an RLC PDU containing the pollinginformation caused by the last RLC PDU trigger undergoes resegmentedretransmission, the polling information should be included in the lastsegment 1425 to best meet the purpose of the polling information.

However, if the polling information is caused by the periodic trigger, apurpose of the polling information is that the transmitter periodicallyreceives a reception status report. Since the situation where an RLC PDUcontaining the polling information should undergo retransmission meansthat the transmitter has failed to receive a reception status report atits first intended time, it is preferable to retransmit the pollinginformation as soon as possible. Therefore, when the RLC PDU containingthe polling information caused by the periodic trigger is subject toresegmented retransmission, the polling information is contained in thefirst segment 1415.

If the polling information is caused by the window trigger, a purpose ofthe polling information is to prevent overflow of the transmissionbuffer. In sum, the purpose of the window trigger means that whenoverflow of the transmission buffer is expected within a short time asthe amount of data stored in the transmission buffer exceeds apredetermined ratio, the transmitter discards from its transmissionbuffer the RLC PDUs that a receiver has successfully received, dependingon a received reception status report. Therefore, if the transmitter hasfailed to receive a reception status report message responsive to thepolling information caused by the window trigger, the transmitter needsto rapidly retransmit the polling information to rapidly receive a newreception status report. Thus, when the RLC PDU containing the pollinginformation caused by the window trigger is subject to resegmentedretransmission, the transmitter includes the polling information in thefirst segment 1415.

FIG. 15 is an overall signal flow diagram according to the fourthembodiment of the present invention.

In a mobile communication system including a receiver 1505 and atransmitter 1510, the transmitter transmits an RLC PDU containingpolling information (as in Step 1515) if a polling triggering conditionis satisfied. An occasion where the transmitter should performresegmented retransmission on the RLC PDU may happen (as in Step 1520),when the amount of transmission resources allocated to the transmitteris insufficient even though the transmitter should retransmit the RLCPDU, because (i) it has received an HARQ NACK signal for the RLC PDU,(ii) it has failed in the transmission of the RLC PDU in an HARQ level,or (iii) it has failed to receive a reception status report until apolling timer expires.

The terminal (or transmitter) checks a condition which has generated thepolling information of the RLC PDU that should undergo resegmentedretransmission, and if it is determined that the polling information wascaused by the last RLC PDU trigger, the transmitter includes the pollinginformation in the last segment of the RLC PDU before transmission (asin Step 1530). If the polling information of the RLC PDU undergoingresegmented retransmission is caused by the periodic trigger or thewindow trigger, the transmitter includes the polling information in thefirst segment of the RLC PDU before transmission (as in Step 1535).

FIG. 16 is a flowchart illustrating an operation of a transmitteraccording to the fourth embodiment of the present invention.

In step 1605, a need occurs for resegmented retransmission of an RLC PDUcontaining polling information. In step 1610, the transmitter checks atrigger of the polling information included in the RLC PDU which issubject to resegmented retransmission. That is, the transmitter checksby which polling triggering condition the polling information wascaused.

The transmitter checks in step 1615 if the trigger of the pollinginformation is the last PDU trigger, and if the trigger is the last PDUtrigger, the transmitter proceeds to step 1620. However, if the triggeris the periodic trigger or the window trigger other than the last PDUtrigger, the transmitter proceeds to step 1625.

In step 1620, the transmitter performs resegmented retransmission on theRLC PDU in such a manner that it includes polling information in thelast segment and starts a polling timer if the last segment issuccessfully transmitted.

In step 1625, the transmitter performs resegmented retransmission on theRLC PDU in such a manner that it includes polling information in thefirst segment and starts the polling timer if the first segment issuccessfully transmitted.

Fifth Embodiment

The fifth embodiment of the present invention provides a method andapparatus for starting a polling timer at the time that the first packetis received from the opposite RLC device after transmitting a pollingPDU. The polling timer is generally started when the polling PDU issuccessfully transmitted.

FIG. 17 is an overall signal flow diagram according to the fifthembodiment of the present invention.

Referring to FIG. 17, if a lower layer notifies that a packet containinga polling PDU has been successfully transmitted (as in Step 1720), atransmitter starts a polling timer, and retransmits the pollinginformation (as in Step 1740) if the transmitter receives no receptionstatus report before the polling timer expires.

In the mobile communication system to which base station-basedscheduling is applied, like in LTE, even though a receiver has normallyreceived a polling PDU, the receiver cannot immediately transmit areception status report message. The receiver should be allocated, froma scheduler, transmission resources over which it will transmit thereception status report, and if a logical channel to which the receiverbelongs has a low priority, a scheduling delay 1730, which is a delayoccurring when the transmission resources are allocated, can have a verylarge value. The scheduler performs scheduling taking into account theamount of data and the priority of the data at an arbitrary time, andgenerally allocates transmission resources first to the high-prioritydata. If the amount of transmission data is not so great at an arbitrarytime, transmission resources can be allocated even to the low-prioritydata with a short time. However, if the amount of transmission data isgreat, a long time may be required for allocating transmission resourcesto the low-priority data. Since the scheduling delay suffers aconsiderable change in this way, it is almost impossible to previouslyestimate its value.

The receiver transmits a reception status report message (as in Step1735) only after suffering the scheduling delay, and if the pollingtimer is set shorter than the scheduling delay, the polling informationmay be unnecessarily retransmitted (as in Step 1740).

Since the situation where an RLC device of an arbitrary logical channelhas received a packet from the opposite RLC device after transmittingpolling information means that transmission resources have beenallocated to the opposite RLC device as the scheduling delay haselapsed, in the fifth embodiment of the present invention, the RLCdevice starts the polling timer after it receives the first RLC PDU fromthe opposite RLC device.

FIG. 18 is a flowchart illustrating an operation of an RLC transmitteraccording to the fifth embodiment of the present invention.

If an RLC device successfully transmits an RLC PDU containing pollinginformation in step 1805, i.e., if a packet containing a polling PDU issuccessfully transmitted in an HARQ level, the RLC device proceeds tostep 1810 where it waits until a predetermined time T3 elapses. SinceHARQ is applied for RLC PDU transmission/reception, there is a variabletransmission delay according to the number of HARQ retransmissions. Theelapsed time of T3 is for compensating for the transmission delay forthe RLC PDU that the opposite RLC device transmitted. In other words,the RLC device waits for T3 to thereby prevent the polling timer frombeing started by the RLC PDU whose transmission was started from theopposite RLC device when a polling PDU is being transmitted.

After T3 has elapsed, if the terminal (or RLC device) receives an RLCPDU from the opposite RLC device at an arbitrary time in step 1815, theRLC device proceeds to step 1820. The term ‘opposite RLC device’ meansanother RLC device that receives an RLC PDU transmitted by the RLCdevice and transmits an RLC PDU to the RLC device, and the opposite RLCdevice belongs to the same logical channel as that of the RLC device. Instep 1820, the RLC device determines if the received RLC PDU is areception status report message or includes a reception status reportmessage. If the received RLC PDU is a reception status report message orincludes a reception status report message, the RLC device proceeds tostep 1825, and otherwise, proceeds to step 1830.

In step 1825, the RLC device, since it has received a reception statusreport message, determines that polling information has beensuccessfully transmitted, and then ends the process.

In step 1830, the RLC device starts the polling timer, and then proceedsto step 1835 where the RLC device determines if a reception statusreport message is received before the polling timer expires. If noreception status report message is received before the polling timerexpires, the RLC device retransmits the polling information in step1840. If a reception status report message is received before thepolling timer expires, the RLC device proceeds to step 1825 where itdetermines that the polling information has been successfullytransmitted, and then ends the process.

Sixth Embodiment

The sixth embodiment of the present invention provides a method forfirst resegmenting the last part of a polling PDU and then includingpolling information in the resegmented PDU before transmission duringresegmented retransmission of the polling PDU.

When a polling PDU undergoes resegmented retransmission as the pollingtimer expires, it is general rule to include the polling information inthe last segment. The expiration of the polling timer means a loss ofthe polling PDU or a loss of STATUS REPORT.

If the polling PDU was lost, it is preferable to retransmit the entirepolling PDU. However, if the polling PDU was normally transmitted butthe STATUS REPORT was lost, it is preferable to transmit only a part ofthe polling PDU, rather than transmitting the entire polling PDU.

The sixth embodiment of the present invention first resegments the lastpart of a payload before transmission rather than first resegmenting thefirst part of the payload as in the normal resegmented retransmission,if it should perform resegmented retransmission on a polling PDU due tothe insufficient account of allocated transmission resources when itshould retransmit the polling PDU for an arbitrary one of the foregoingreasons.

FIG. 19 is a diagram for a description of an example of the sixthembodiment of the present invention.

Referring to FIG. 19, after transmitting a polling PDU 1905 with anX-byte payload, a terminal has a need to retransmit the RLC PDU for anarbitrary reason. In this case, if the terminal can include only aY-byte payload therein because of insufficient transmission resourcesallocated for the RLC PDU retransmission, i.e., if the terminal shouldresegment the polling PDU in an RLC PDU with a Y-byte payload for itsretransmission, the terminal generates a resegmented RLC PDU 1910containing the last Y bytes in the payload of the original polling PDU,and includes polling information 1915 in the RLC PDU beforetransmission.

Since it is uncertain whether the retransmission of the polling PDU iscaused by a loss of the polling PDU or by a loss of STATUS REPORT, theterminal does not transmit the remaining segment, i.e., the segmentcontaining the remaining payload 1920 except for the previouslytransmitted Y bytes among the X original bytes, until it receives RLCSTATUS REPORT.

FIG. 20 is a signal flow diagram illustrating an operation of a terminalaccording to the sixth embodiment of the present invention.

Referring to FIG. 20, if there is a need for retransmission of a pollingPDU in step 2005 as a polling timer expires, a terminal performs anecessary operation of sending a request for transmission resources to abase station for the retransmission. If transmission resources areallocated from the base station, the terminal determines in step 2010whether there is a need for resegmented retransmission.

If it is determined in step 2010 that a size of an RLC PDU transmittableover the allocated transmission resources is less than a size of thepolling PDU to be retransmitted, meaning that there is a need forresegmented retransmission, the terminal proceeds to step 2020.

In step 2020, the terminal generates a resegmented PDU by resegmentingthe last Y bytes of the payload of the polling PDU to be retransmitted.‘Y’ corresponds to a payload size of the RLC PDU transmittable over theallocated transmission resources. In step 2025, the terminal includespolling information in the generated resegmented PDU. For example, theterminal sets a polling bit of the RLC PDU header as ‘yes’.

In step 2030, the terminal transmits the resegmented PDU and then endsthe process. Thereafter, even though transmission resources areallocated, the segment left after the resegmentation is notretransmitted unless an RLC STATUS REPORT requesting retransmission ofthe segment left after the resegmented retransmission is received.

However, if it is determined in step 2010 that the size of the RLC PDUtransmittable over the allocated transmission resources is greater thanor equal to the size of the polling PDU to be retransmitted, theterminal proceeds to step 2015 where it retransmits the polling PDU, andthen ends the process.

As is apparent from the foregoing description, the present inventionallows small-sized packets to be transmitted together if possible,rather than to be frequently and individually transmitted and receivedover a radio channel, thereby contributing to an increase in efficiencyof the radio transmission resources. In addition, the present inventionguarantees transmission reliability of the individually transmittedupper layer packets without using a reception status report, therebycontributing to an increase in efficiency of the radio transmissionresources.

While the invention has been shown and described with reference to acertain preferred embodiment thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

What is claimed is:
 1. A method for transmitting data by a transmittingapparatus in a communication system, the method comprising:transmitting, to a receiving apparatus, a data unit, wherein, if thedata unit is a last data unit to be transmitted, the data unit comprisesfirst polling information; receiving, from a receiving apparatus, a NACKsignal corresponding to the data unit; segmenting the data unit into aplurality of segments, if an amount of available resources is less thanan amount of resources required for retransmitting the data unit; andtransmitting, to the receiving apparatus, a segment among the pluralityof segments, wherein, if the segment is a last segment to betransmitted, the segment comprises second polling information.
 2. Themethod of claim 1, wherein the first polling information indicates torequest the receiving apparatus to transmit a status report.
 3. Themethod of claim 1, wherein the second polling information indicates torequest the receiving apparatus to transmit a status report.
 4. Themethod of claim 3, wherein the first polling information is differentfrom the second polling information.
 5. The method of claim 3, furthercomprising: starting a timer after transmitting of the data unitcomprising the first polling information; and if the NACK signalcorresponding to the data unit is not received until expiry of thetimer, retransmitting the data unit comprising the first pollinginformation.
 6. An apparatus for transmitting data in a communicationsystem, the apparatus comprising: a transceiver configured to transmit,to a receiving apparatus, a data unit, wherein, if the data unit is alast data unit to be transmitted, the data unit comprises first pollinginformation, and receive, from a receiving apparatus, a NACK signalcorresponding to the data unit; and a controller configured to segmentthe data unit into a plurality of segments, if an amount of availableresources is less than an amount of resources required forretransmitting the data unit, and control the transceiver to transmit,to the receiving apparatus, a segment among the plurality of segments,wherein, if the segment is a last segment to be transmitted, the segmentcomprises second polling information.
 7. The apparatus of claim 6,wherein the first polling information indicates to request the receivingapparatus to transmit a status report.
 8. The apparatus of claim 6,wherein the second polling information indicates to request thereceiving apparatus to transmit a status report.
 9. The apparatus ofclaim 8, wherein the first polling information is different from thesecond polling information.
 10. The apparatus of claim 8, wherein thecontroller is further configured to: start a timer after transmitting ofthe data unit comprising the first polling information; and if the NACKsignal corresponding to the data unit is not received until expiry ofthe timer, control the transceiver to retransmit, to the receivingapparatus, the data unit comprising the first polling information.